The present invention relates to polyolefin alloys that are specially formulated to be readily plated with various metals. These compositions can be easily processed into molded articles by molding methods, such as injection, and then plated with metal, such as to provide a decorative or functional finish. More particularly, these compositions are blends of an ethylene component, acrylonitrile-butadiene-styrene polymer component, and styrene monoolefin copolymer component, which blends have excellent platability as well as preferably having superior physical properties including enhanced stiffness and toughness.
A substantial market exists for metal plated thermoplastics, particularly for applications in the automotive industry. The current overwhelming choice of plastic materials for such applications include acrylonitrile-butadiene-styrene (ABS) engineered resins, either alone or in polymer alloys with polycarbonates. These materials are useful due to the degree of unsaturation and polarity of the plastic, which render it suitable for metal plating.
There are disadvantages in the use of ABS resins. The platable grades are relatively expensive, while the final properties of the metal plated plastic are not all that are desired. In an effort to improve upon the properties of the plastic, polyolefin blends have been utilized as alternatives. These blends include thermoplastic polyolefins and are widely used in interior and exterior automotive applications, such as bumpers, body panels, fascia, and the like. Many of these are decorated by full or partial painting for enhanced visual or functional effects.
Polyolefins, however, are difficult to plate with metal, due to a lack of polarity or unsaturation. While it can be plated using special electroplating conditions, it generally is not because of cost and availability considerations. Since polyolefins, such as polyethylene homopolymers or copolymers, have certain performance advantages compared to ABS, the modification of this material to improve platability has been studied.
U.S. Pat. No. 3,655,433 discloses polyolefin alloys that are suitable for electroplating, wherein the adhesion of metal to the compositions is enhanced by incorporating into the composition a metal resinate. Crystalline polyolefins are modified with metal resins to improve the adhesion of metal thereto.
U.S. Pat. No. 3,663,260 discloses a metallizable polyolefin superimposed on a metal layer, wherein the polyolefin contains a finely divided talc having a platey (minacious) or massive (granular) particle shape. The talc filled polyolefin composition may be metallized by electroplating or other metallizing processes to form metallized shaped articles.
U.S. Pat. No. 4,038,042 discloses polyolefin-based compositions that are blends of particular proportions and types of polyethylene, low polarity rubber, highly conductive carbon black, polypropylene and optional mineral additives that provide electroplating to give adherent, plated surfaces.
U.S. Pat. No. 4,199,491 discloses polyolefin resin compositions including block copolymers of polypropylene and polyethylene. In particular, improved plating by the high-chrome etching-catalyst method can be accomplished by blending a compound containing a cyano group with a mixture of polyolefin resin and inorganic filler. Unsaturated carboxylic acids or rubbers are also blended therein.
U.S. Pat. No. 6,027,817 discloses a resin composition based on a styrenic polymer having a syndiotactic configuration, which resin also contains elastomers, thermoplastic resins and fillers that are soluble in oxidizing agents. Glass fibers and fumaric-acid-modified polyphenylene ether may also be blended therein.
Despite these patents, there still exists a need for olefinic materials containing ethylene homopolymers or copolymers that are readily electroplatable utilizing conventional processes to obtain parts or components that are visually appealing as well as functional. The present invention satisfies this need.
The invention encompasses platable polyolefin blends including an ethylene component that includes polyethylene, high density polyethylene, low density polyethylene, linear low density polyethylene, or a combination thereof, a polymeric compatibilizer including at least one styrene monoolefin copolymer (e.g., a hydrogenated styrenic copolymer) present in an amount sufficient to facilitate adhesion between the components of the polyolefin blend, and an ABS resin component of an acrylonitrile-butadiene-styrene resin or a blend of styrene-acrylonitrile resin with a diene, the ABS resin component being present in an amount sufficient to render the polyolefin blend suitable for electroplating. In one embodiment, the ethylene component includes an ethylene homopolymer, while in another embodiment the ethylene component includes an ethylene copolymer.
The invention also relates to platable polyolefin blends including an ethylene component, a polymeric compatibilizer that includes at least one styrene monoolefin (e.g., a hydrogenated styrenic copolymer), wherein the styrenic copolymers is present in an amount sufficient to facilitate adhesion between the components of the polyolefin blend, and an ABS resin component of an acrylonitrile-butadiene-styrene resin or a blend of styrene-acrylonitrile resin with a diene. Suitable ethylene components include one or more polyethylenes, high density polyethylenes, low density polyethylenes, or a combination thereof The ABS resin component is present in an amount sufficient to render the polyolefin blend suitable for electroplating.
In one embodiment, the at least one styrene monoolefin copolymer includes at least one hydrogenated styrenic copolymer. Advantageously, the styrene monoolefin copolymer includes one or more random or block copolymers of styrene and a hydrogenated olefinic component; random copolymers of ethylene and styrene; or combinations thereof. The styrene monoolefin copolymers preferably include styrene-ethylene/butylene-styrene (SEBS), styrene-ethylene/butylene, styrene-butylene-butadiene-styrene (SBBS), styrene-ethylene/propylene-styrene, styrene/ethylene-propylene, styrene-ethylene/propylene-styrene-ethylene-propylene, or combinations thereof, and is present in an amount of about 1 to 45 weight percent of the polyolefin blend. In a preferred embodiment, the polymeric compatiblizer includes about 2 to 40 weight percent of a styrene monoolefin copolymer.
The polymeric compatibilizer may optionally include a styrene diolefin copolymer (e.g., a non-hydrogenated styrenic copolymer), which includes block or random copolymers of styrene and an unsaturated olefinic component. Preferably, this copolymer comprises styrene-butadiene (SB), styrene-butadiene-styrene, styrene-isoprene, styrene-isoprene-styrene, or mixtures thereof.
Advantageously, the compatibilizer can be a block or random copolymer including at least two different block copolymers of styrene-ethylene/butylene-styrene, styrene-ethylene/propylene-styrene, styrene-ethylene/butylene, styrene/ethylene-propylene, styrene-butadiene-styrene, styrene-butylene-butadiene-styrene, styrene/butadiene, styrene-ethylene/propylene-styrene-ethylene/propylene, styrene-isoprene, styrene-isoprene-styrene, or mixtures thereof, so long as at least one of the polymers is hydrogenated. Additionally, the compatibilizer can comprise copolymers of ethylene and styrene, or random copolymers of styrene, ethylene, butylene, propylene, or mixtures thereof.
The platable polyolefin blend optionally but preferably includes a toughening agent of a substantially amorphous copolymer or terpolymer of ethylene and an alpha olefin. In particular, the substantially amorphous copolymer or terpolymer includes but is not limited to ethylene, an alpha olefin, and a diene or mixtures thereof. The platable polyolefin blend optionally includes a propylene-containing polymer formed from a semi-crystalline homopolymer of propylene or a copolymer of propylene with ethylene or an alpha-olefin.
In these blends, the ethylene homopolymer component is typically present in an amount of about 20 to 80 weight percent, the polymeric compatibilizer is present in an amount of about 1 to 45 weight percent, and the ABS resin component is present in an amount of about 2 to 60 weight percent of the alloy. When present, the substantially amorphous copolymer or terpolymer of ethylene and an alpha olefin is used in an amount of about 0.01 to 30 weight percent. The optional propylene-containing polymer formed from a semi-crystalline homopolymer of propylene or a copolymer of propylene with ethylene or an alpha-olefin is used in an amount of up to about 20 weight percent.
Inorganic fillers are optionally included in amounts up to about 35 weight percent. When an inorganic filler is included, it is typically present in an amount of about 0.01 to 35 percent by weight. Preferably, however, the invention includes an inorganic filler present in an amount of about 5 to 20 percent by weight of the polyolefin blend. In another embodiment, the polyolefin blend is substantially free of inorganic filler, or preferably even completely free of inorganic filler, which facilitates downstream processing of the blend. xe2x80x9cSubstantially free,xe2x80x9d as used herein, refers to less than about 5 weight percent, preferably less than about 1 weight percent, and more preferably less than about 0.1 weight percent filler in the blend. In one preferred embodiment, the blend is ductile at 0xc2x0 C.
The invention also relates to a molded article of manufacture including the polyolefin blends described above, as well as molded articles in the form of automotive components. The invention further encompasses molded articles, such as automotive components, that further include a metal deposit disposed over a portion thereof.
The invention also encompasses a platable polyolefin blend including an ethylene component present in an amount of about 20 to 80 weight percent and including polyethylene, high density polyethylene, low density polyethylene, linear low density polyethylene, or a combination thereof, a polymeric compatibilizer comprising at least one styrene monoolefin copolymer present in an amount of about 1 to 45 weight percent to facilitate adhesion between the components of the polyolefin blend, an ABS resin component of an acrylonitrile-butadiene-styrene resin or a blend of styrene-acrylonitrile resin with a diene, the ABS resin component being present in an amount of about 2 to 60 weight percent to render the polyolefin blend suitable for electroplating, and optionally, a toughening agent of a substantially amorphous copolymer or terpolymer of ethylene and an alpha olefin present in an amount of about 0.01 to 30 weight percent.
The invention further encompasses a process for preparing a plated polyolefin article by blending an ethylene component, a polymeric compatibilizer including at least one styrene monoolefin present in an amount sufficient to facilitate adhesion between the components of the polyolefin blend, and an ABS resin component of an acrylonitrile-butadiene-styrene resin or a blend of styrene-acrylonitrile resin with a diene, the ABS resin component being present in an amount sufficient to render the polyolefin blend suitable for electroplating, to form a blend, forming the blend into an article having a desired form, shape, and an exterior surface, depositing an initial conductive metal onto at least a portion of the surface of the article, and plating a second metal over the polyolefin article.
In a preferred embodiment, the polyolefin article is formed by molding the blend. In another preferred embodiment, the second metal is deposited by electroplating or by vacuum deposition. In a particular embodiment, the initial conductive metal is copper, a nickel/phosphorus alloy, or a mixture thereof. In a particular embodiment, the second metal includes at least one of nickel, copper, and chromium, or a mixture thereof.
In a particular embodiment, the plated polyolefin article is prepared in the form of a molded article. In a preferred embodiment, the molded article is an automotive component.